Thin-lead mechanical pencil



L. WITTROCK THIN-LEAD MECHANICAL PENCIL Dec. 1, 1970 2 Sheets-Sheet 1 Filed Oct; 16, 1968 Ludwig Wiffrock m V/jN'lUA L. WITTROCK THIN-LEAD MECHANICAL PENCIL Dec. 1,]1970 Q'Sheets-Sheet 2 Filed Oct. 16. 1968 v1!iz 1 I I IflI/fiIf A/II I I I I I/II I I\ "w "I w WW W] L Attorney United States Patent 3,544,228 THIN-LEAD MECHANICAL PENCIL Ludwig Wittrock, 121 Breddenrampstrasse, 437 Marl, Germany Filed Oct. 16, 1968, Ser. No. 767,964

' Int. Cl. B43k 21/06 US. Cl. 401-82 6 Claims ABSTRACT OF THE DISCLOSURE A slidable insert projecting from a cylindrical sleeve has a narrow center bore to accommodate a thin lead, the sleeve containing a pusher member with two or more radial ribs bearing upon the inner sleeve periphery; the rear part of the insert is provided with guide formations which form clearances for the ribs and slidably engage the pusher member to stabilize it against bending.

My present invention relates to a mechanical pencil using thin leads for the tracing of fine lines without any sharpening of the lead point. By thin lead is meant a conventional graphite rod whose diameter is a fraction of a millimeter, usually 0.5 mm. or less.

Ordinary mechanical pencils, in which 7 a relatively heavy lead is axially slidable in a central channel of a generally cylindrical filter, use a pusher rodof a diameter substantially equal, to that of the lead for progressively extruding the latterfrom the holder. With thin leads, as defined a ve, apusher rod of correspondingly reduced diameter would be liable to bend along that part of its length which is not received in the lead channel. Thus, prior structures of "mechanical pencils with thin leads either required pusher rods of expensire, nonbending materials or'had to belimited to relatively short stroke lengths for the pusher member. a

The general object of 'my present invention is to provide an improved pencil construction of this type which avoids the aforestated drawbacks and facilitates the dispensing of thin lead of considerable length by a simple and inexpensive mechanical arrangement.

This object is realized, pursuant to my present invention, by the provision of a sleeve slidably receiving a tubular insert whose bore accommodates a thin lead, the diameter of this bore being thus less than 1 mm., the rear part of the sleeve containing a pusher member having two or more radial ribs bearing upon the inner sleeve periphery; the tubular insert has guide formations which define clearances for the pusher member with its ribs and which guide this member into engagement with the inner end of the lead, the permanent interengagement of the pusher member and the guide formations preventing any substantial deformation of the pusher member even when the latter is in its initial position of maximum withdrawal from the sleeve.

Although the invention may be realized with a single pair of coplanar ribs merging into a blade-shaped pusher member, greater stability is obtained with three or more ribs which are angularly equispaced along the inner sleeve periphery. Generally, the thickness of these ribs should be somewhat less than the diameter of the lead, e.g. 0.1 to 0.3 mm. if the lead diameter is 0.3 to 0.5 mm., yet a rod or wire substantially equal in diameter to the lead may be provided at the junction of these ribs to act as a pusher pin. In such a case, the guide formations of the tubular insert may be radial ribs or fins rigid with that insert and angularly staggered with reference to the ribs of the pusher member to bear upon the exposed pin surface, this construction resulting in guidance of the pusher member with minimum friction; in other instances, these guide formations may simply be radial slits in the 'ice rear part of the insert, these slits being just wide enough to accommodate corresponding ribs of the pusher mem her with sliding fit.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is an axial sectional view of a mechanical pencil according to the invention;

FIG. 2 is a view similar to FIG. 1 taken at right angles thereto;

FIG. 3 is a side-elevational view of a tubular insert forming part of the structure of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view taken on the line IV-IV of FIG. 2;

FIG. 5 is a cross-sectional view taken on the line V-V of FIG. 3;

FIG. 6 is a view generally similar to FIG. 1, illustrating another embodiment;

FIG. 7 is a cross-sectional view taken on the line VIIVII of FIG. 5;

FIG. 8 is a view similar to FIG. 5, illustrating a further modification; and

FIG. 9 is a view similar to FIG. 7, relating to the modification of FIG. 8.

The mechanical pencil used in FIGS. 1-5 comprises a generally cylindrical sleeve 1 with a bore 12 slidably receiving, with frictional fit, a tubular insert 4 having a lead 5 slidably fitted into its own bore 3. Lead 5 is asblade, with a thickness slightly less than the diameter of lead 5, is fixedly mounted in lateral grooves 11 of sleeve 1 and is held in position by a handle 9 threadedly secured at 10 to the rear end of the sleeve; handle 9 may be of any convenient shape and may carry the usual clip 13 for attachment to a coat pocket. Tube 4 is divided at its rear portion into two substantially semicylindrical segments operated by a pair of diametrically opposite longitudinal slits 6 which are only slightly wider than blade 2 and serve to guide same into contact with lead 5, these slits being open toward the bore 3 of the tube.

In its initial position, illustrated in dot-dash lines in FIG. 1, tube 4 is withdrawn from sleeve 1 to an extent maintaining a slight overlap between the grooves 11 and the slits 6 so that the pusher blade 2 is guided by both the slits and the grooves, being thereby held against deformation despite its limited thickness. The user then places the rounded end of tube 4 onto the writing surface S, holding the pencil at an acute angle thereto sub stantially as illustrated in FIGS. 1 and 2, and exerts just enough pressure upon handle 9 and sleeve 1 to let the tip of lead 5 emerge from tube 4 as a virtual continuation of the outer tube surface, thereby enabling the tracing of fine lines without any need for resharpening or periodically advancing the lead. The central portion or core of blade 2, flanked by the rib-like elements guided in grooves 11, slides in bore 3 to displace the lead 5 relatively to tube 4 as the lead is used up.

In the embodiment of FIGS. 6 and 7, insert 4' is a solid tube without lateral slits but with an array of four angularly equispaced radial ribs 8' extending rearwardly within sleeve 1 to define a central channel in line with bore 3 and of the same diameter. A similar array of ribs 7' in sleeve 1', offset by 45 from the ribs 8', bear upon a central pusher pin 2'. Like the pusher member 2 of the first embodiment, pin 2' and its supporting ribs 7', 8' may be metallic, the sleeve 1 and the tube 4' being again shown to consist of plastic material. In the initial position illustrated in FIG. '6, the stationary ribs 7 and the movable ribs or fins 8' overlap slightly for joint guidance ofthe pin-2' whose diameter may be equal to or slightly less than that of lead 5', e.g. 0.5 mm. Ribs 7' could also be integral with pin 2. The operation is similar to that describedin connection with FIGS.'l and 2.

' FIGS. 8 and 9 illustrate a modification according to which the operative part of the pusher memberis constituted by the junction of three radial ribs 7" spaced 120 apart, with omission of a separate rod or pin as shown at 2' in FIGS. 6and 7; ribs 7" fit in radial slits 6" of tube 4" which is thereby divided into three cylinder segments, these slits emanating from the center bore 3 of the tube.

Naturally, a rod orwire similar to pin 2', slightly exceeding in diameter the width of the associated ribs 7", could be disposed'at the junction of these ribs in line with the bore 3"; by the same token, such a rod or wire could alsobe the core portion'of the flat pusher member 2 of FIGS. 1-3. Conversely, the rodless arrangement of FIG. 9 could also be extended to a pusher with four or more ribs, with replacement of the ribs 8' of FIGS. 5 and 7 by a corresponding number of slits (simi lar to slit 6") in an otherwise solid rear portion of the slidable tube.

The external rounding (FIGS. 1 and 2) or beveling of the tip of insert 4 or 4' provides a contour whose generatrices converge at a point along the tube axis forwardly of its front end to ensure a continuous feed-out of lead 5 or 5' when the implement is held at a suitable angle to the writing surface.

I claim: 1

1. A mechanical pencil comprising a forwardly open sleeve, a tubular insert slidably projecting from the forward end of said sleeve, said insert having a bore slidably accommodating a thin lead, and a pusher member in a rear part of said sleeve comprising a central core flanked by a plurality of elongate, peripherally spaced parallel.

elements bearing upon the inner sleeve periphery, said core being slidably received in said bore, said insert having a rear part in said sleeve provided with longitudinal guide formations overlapping said elements and forming peripherally spaced clearances therefor communicating with said bore, said formations slidably engaging said pusher member while enabling said core to exert forward pressure upon said lead in response to relative axial displacement of said sleeve and said insert.

2. A pencil as defined in claim 1 wherein said elements are ribs of a width less than the diameter of said bore and said core is rod at the junction of said ribs, said rod having a diameter substantially equal to the diameter of said bore and being receivable therein.

3. A pencil as defined in claim 12 wherein said guide formations include an array of radial fins angularly staggered with reference to said ribs, said fins defining a centralchannel in line with said bore and of a diameter equal to that of said rod.

4. A pencil as defined in claim ,1 wherein said guide formations are cylinder segments separated by radial slits UNITED STATES PATENTS 1,406,585 2/1922 Sawyer 401-82X 1,816,545 7/1931 Porter 401-82 2,819,700 1/1958 Spector 40158 3,139,982 7/1964 Aversa 401-82 2,034,133 3/1936 Drecfge s 401-82 FOREIGN PATENTS 523,149 4/1955 Italy 401 82 LAWRENCE CHARLES, Primary Examiner 

